This invention relates to a navigation system for an automatically guided vehicle, and a method of navigating an automatically guided vehicle. Characteristics of the system provide for both steering and distance measurement and control. The applicant is Assignee of U.S. Pat. No. 4,626,995 which discloses an apparatus and method for optical guidance of an automatic guided vehicle. In the '995 patent, a computer determines the cartesian coordinates of a single light source through a camera attached to the vehicle. Distance is determined by calculating the angle between the known height of the camera lens above the surface on which the vehicle travels and the known height of the light source above the surface on which the vehicle travels. The angle, or azimuth, is converted by the computer into a distance value.
The invention in the '995 patent performs well in many environments. However, in conditions where the surface on which the vehicle travels is irregular the computed angle is subject to error. In addition, many applications involve the placement and removal of heavy cargo onto and off of the vehicle. The changes in the weight on the vehicle cause the level of the camera to change due to, for example, tire and shock absorber compression, causing error in distance computation. In such instances, a wire guided system has been the usual alternative. The invention disclosed in this application avoids these problems and offers additional advantages such as the ability to guide over greater distances. The invention is particularly useful in environments such as hospitals, food and drug processing plants, offices, elevators, and areas with steel floors, ceramic tile floors or similar structures which cannot accept wire guidance-type systems. However, the system is so flexible that it can be used in combination with a wire-guided system, if desired.